The invention relates to an apparatus for the recognition of codes comprising a light transmitter for the transmission of light signals in the direction of a scanning region, a light receiver for the reception of a light signal remitted from the scanning region, and a control and evaluation unit for the control of the light transmitter and the light receiver and for the determination of a code from the light signal received, with the control and evaluation unit including a trigger circuit which triggers the determination of a code. The invention further relates to a method for the recognition of codes by means of a code reader, in which light signals are transmitted by a light transmitter in the direction of a scanning region, the light signals are remitted from the scanning region to a light receiver, and the output signal of the light receiver is supplied to a control and evaluation unit for the control of the light transmitter and of the light receiver and for the determination of a code from the light signal received, with the determination of a code being triggered by a trigger circuit associated with the control and evaluation unit.
It is known in accordance with the prior art to use an external light barrier as the trigger circuit which is in a position to detect articles transported on a conveyor belt, for example, and to trigger the start of a read gate in dependence on the detection of an object, with a code determination by the code reading taking place within said read gate. It is achieved in this manner that an attempt is only made to determine a code when there is also actually an object possibly bearing a code within the scanning region.
The fact is disadvantageous in the prior art that the code reader and the light barrier represent two separate units which have to be installed in a mutually spaced manner so that a comparatively large amount of room is taken up for the total arrangement and, furthermore, an installation of the two units exactly adjusted to one another is also required.
An object of the invention consists of further developing an apparatus or a method of the kind initially mentioned such that both the adjustment effort and the installation room taken up are reduced.
This object is satisfied with an apparatus of the invention in that a distance determination unit or image detection unit for the detection of an object present in the scanning region and acting on the trigger circuit is integrated into the apparatus. The object is satisfied by a method of the invention in that the trigger circuit is acted on by a distance determination unit or image detection unit integrated in the code reader for the detection of an object present in the scanning region.
In accordance with the invention, the external light barrier known from the prior art is therefore replaced by a distance determination unit or image detection unit which is integrated into the apparatus or into the code reader. As the code reader and the distance determination unit or image detection unit are thus formed as a single assembly, the room requirements taken up can be reduced. Moreover, all required adjustment procedures between the code reader and the distance determination unit or image detection unit can be made during the mounting of the total assembly so that respective adjustment work in the installation of the assembly on site is omitted.
Furthermore, the distance determination unit or image detection unit provided in accordance with the invention is able to provide more detailed information on a detected object than was possible with a light barrier of the prior art which was only able to report whether the object is present or not. In accordance with the invention, namely, information can additionally be determined and evaluated on the size, shape, direction of movement, speed, color, etc. of the object.
Moreover, maintenance and service as well as a replacement of the total arrangement is simplified by the design in accordance with the invention of the total arrangement as only one single assembly.
It is advantageous for the light transmitter, the light receiver, the control and evaluation unit of the code reader and the distance determination unit or the image detection unit to be arranged in a common housing. The arrangement in a common housing can make it possible, for example, that only one light transmitter and/or only one light receiver are provided which are both used by the distance determination unit or image detection unit and controlled by the control and evaluation unit for the code determination. In this manner, the realization of the total arrangement with a single light transmitter and a single light receiver is sufficient, which reduces the manufacturing costs, on the one hand, and makes adjustment work between the code determination unit and the distance determination unit or image detection unit absolutely superfluous since the use of a common light transmitter and of a common light receiver ensures that both units cover the same field of view or the same scanning region.
Alternatively, however, it is also possible to use more than one light transmitter and only one light receiver, more than one light transmitter and more than one light receiver, or only one light transmitter and more than one light receiver. If a plurality of light transmitters or light receivers are provided, one light transmitter or light receiver can be associated with the distance determination unit or image detection unit and a further light transmitter or light receiver be used by the code reader.
Likewise, a plurality of light transmitters, which work, for example, with different wavelengths, can be used both by the distance determination unit or image detection unit and by the code reader, and/or a plurality of light receivers, which have, for example, different focus settings, can be used both by the distance determination unit or image detection unit and by the code reader.
The ending of the code determination preferably takes place in dependence on the distance values or image values supplied by the distance determination unit or image detection unit so that, ultimately, a time-wise restricted read gate is generated in dependence on these supplied values. This read gate can consequently be set such that it is always open when an object is in the scanning region.
It is alternatively also possible to end the read gate for the code determination after a predetermined time interval subsequent to the triggering of the code determination. This time interval can be set in this respect such that the read gate extends with high probability over that time period in which an object is located in the scanning region.
It is of advantage if a signal output is provided for the making available of information with respect to an object present in the scanning region determined from the supplied distance value or image values. Information on a recognized object can be transmitted to further apparatuses of the same kind or of a different kind via this signal output. A specific application will still be explained as part of the figure description.
It is furthermore preferred for a unit to be provided for the determination of the speed of an object moving in the scanning region from the distance values or image values supplied in a time sequence by the distance determination unit or image detection unit. It can, for example, be determined from speeds determined with such a unit when a read gate begins and ends in a meaningful manner, provided that the object recognized moves at least at largely constant speed.
The distance determination circuit integrated into the code reader in accordance with the invention can preferably act on a focusing unit for focusing an optical transmission and/or reception system associated with the light transmitter and/or with the light receiver on an object present in the scanning region. It can thus be ensured that the focus is always ideally matched to the momentarily present distance between the object and the code reader.
In this respect, the focusing can be initiated before or simultaneously with the triggering of the code determination. If the focusing is initiated before the triggering of the code determination, it is of advantage for the distance between the object and the code reader present at the code determination to be calculated in advance and for the focus to be able to be already correctly adjusted in advance so that the correct focus is already set directly at the start of the code determination.
It is furthermore possible to automatically adjust the focusing unit to different, successive distance values covering all possible read distances during a code determination. This embodiment of the invention is explained in more detail as part of the figure description.
It is of advantage for the distance determination to take place in a part of the scanning region or in the total scanning region such that not only one single distance value, but a two- or three-dimensional distance profile can be determined. The spatial and/or time-wise patterns in which the single distance values of a distance profile are determined can be individually fixed. A rough pattern results in this respect in an increased evaluation speed which, however, is obtained at the cost of accuracy. A finer pattern slows the evaluation speed, but provides higher accuracy.
It is particularly preferred for a two-or three-dimensional background profile to be taught/learned before the code determination and for the difference profile between the momentarily determined two- or three-dimensional distance profile and the taught/learned background profile to be evaluated as part of the code determination. It becomes possible in this way to reliably recognize objects in containers without the container supplying interfering distance values, since the container shape can be taught/learned in advance as a background profile. It is furthermore advantageous that it can also be recognized in the manner described whether an object is located in a container or not, and indeed independent of whether a code can subsequently be read or not.
In the latter case, the difference profile, in particular the minimum value of the difference profile, can be used for the focusing. Trials have shown that the use of the minimum value here, which usually corresponds to the upper side of the object, leads to a good result since the focus is then adjusted as a rule such that a code located on the upper side of an object can be read.
The distance determination unit or image detection unit of the invention is preferably not activated constantly, but only cyclically, so that the individual components of the apparatus, in particular the focusing unit or the light transmitter, which is preferably formed as a laser diode, do not age too quickly due to the interposed pauses.
The invention is explained in the following by means of embodiments with reference to the drawings.